Clutch mode control logic

ABSTRACT

A friction clutch coupling an engine and a gear transmission of a vehicle is controlled by a microprocessor based circuit using logic which defines operating modes according to engine and clutch conditions. During the time of clutch closure, when the vehicle is starting from rest in a startup or launch mode, the throttle or other engine control signal is restrained from quickly responding to the accelerator pedal. This avoids engine overspeeding which results from generating high torque before sufficient clutch capacity has been achieved. The control signal is developed as a function of the pedal position under control of throttle logic which, in turn, is dependent on clutch operating modes defined by the clutch logic. The clutch operating modes are four modes for automatic clutch operation comprising touch point approach mode which prohibits a throttle signal during initial clutch movement, creep mode or startup mode after touch point occurs, and lockup mode for completing clutch closing when low clutch slip is attained. A non-automatic mode is entered before the accelerator pedal is depressed or when engine stall conditions are detected.

This application is a division of application Ser. No. 987,772, filedDec. 9, 1992, now U.S. Pat. No. 5,314,050.

FIELD OF THE INVENTION

This invention relates to an engine and automatic clutch control method,and more particularly to the logic for controlling an automatic clutchas well as engine throttle demand.

BACKGROUND OF THE INVENTION

In recent years there has been a growing interest in increasedautomation in the control of the drive train of motor vehicles, and mostespecially in control of the drive train of large trucks. The use ofautomatic transmissions in passenger automobiles and light trucks iswell known. The typical automatic transmission in such a vehicle employsa fluid torque converter and hydraulically actuated gears for selectingthe final drive ratio between the engine shaft and the drive wheels.This gear selection is based upon engine speed, vehicle speed and thelike. It is well known that such automatic transmissions reduce theeffectiveness of the transmission of power from the engine to the driveshaft, with the consummate reduction in fuel economy and power ascompared with the skilled operation of a manual transmission. Suchhydraulic automatic transmissions have not achieved wide spread use inlarge motor trucks because of the reduction in efficiency of theoperation of the vehicle and added cost.

One of the reasons for the loss of efficiency when employing a hydraulicautomatic transmission is loss occurring in the fluid torque converter.A typical fluid torque converter exhibits slippage and consequent lossof torque and power in all modes. It is known in the art to providelockup torque converters that provide a direct link between the inputshaft and the output shaft of the transmission above certain enginespeeds. This technique provides adequate torque transfer efficiency whenengaged, however, this technique provides no gain in efficiency at lowerspeeds.

It has been proposed to eliminate the inefficiencies inherent in ahydraulic torque converter by substitution of an automatically actuatedfriction clutch. This substitution introduces certain problems notexhibited in the use of the hydraulic torque converters. U.S. patentapplication Ser. No. 772,204, filed Oct. 7, 1991 and entitled "ClosedLoop Launch and Creep Control for Automatic Clutch" teaches theminimization or elimination of torsional oscillations due to compliancein the driveline during clutch engagement by controlling the clutchactuation to effect a smooth engagement. U.S. patent application Ser.No. 772,778, filed Oct. 7, 1991 and entitled "Closed Loop Launch andCreep Control for Automatic Clutch with Robust Algorithm" addresses thesame problem and includes a prefilter to shape the system transientresponse and reduces the need for detailed particularization forindividual vehicles or vehicle models. Each of those disclosures, Ser.No. 772,204 and Ser. No. 772,778, hereby incorporated by reference, isassigned to the assignee of this invention and includes the generationof a clutch control signal which is dependent on the selection of acreep or launch mode.

Still another problem relates to the slow response to the clutchactuation algorithm. Friction clutches exhibit considerable time delaybetween the point when throttle actuation calls for clutch applicationand the point that the clutch develops torque capacity equivalent to theengine torque, so that in the meantime the engine is not restrained andits speed may become excessive. Here a method is proposed whichapproximates the action of a human operator, taking into account thecondition of clutch actuation to coordinate the engine speed with theclutch engagement.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a control methodfor establishing a clutch mode for control of clutch actuation anduseful for control of the throttle or other engine torque demand inputduring clutch engagement.

This invention provides automatic and reliable control of accelerationpedal input to the vehicle engine during initial application of a clutchcontrolled by an automatic clutch actuation controller. This inventionis employed in a combination including an engine, a friction clutch, amulti-speed transmission having a neutral position, at least oneinertially-loaded traction wheel connected to the output of themulti-speed transmission, and an automatic clutch controller.

The clutch controller is provided with inputs comprising acceleratorpedal position, engine speed, transmission input speed, vehicle brakeapplication, and a gear indication and engage/disengage signal from ashift controller, and yields outputs for controlling clutch engagementand for limiting engine torque. The clutch controller determines whetherthe vehicle is starting out in launch mode, wherein the pedal positionis at least 25% of full travel, or creep mode wherein the pedal positionis below 25%. It also determines when, during the engagement of theclutch plates, a touch point occurs and later during clutch closure, itdetermines when the clutch capacity is sufficient to cause enginedeceleration. The controller has four automatic modes and anon-automatic mode. The latter is Auto Mode Off and commands the clutchto be fully disengaged. The automatic modes include Touch Point ApproachMode which commands the clutch to go to the touch point, Creep Modewhich maintains the clutch in a slipping condition at low acceleratorpedal positions, Startup Mode which commands a controlled clutch closureas a function of accelerator pedal position, and Lockup Mode whichcommands full clutch engagement.

Using this mode information, throttle filter logic within the clutchcontroller determines one of four filter states: Launch, Touch PointApproach, Ramp and Direct. In Direct state the output is equal to thepedal position signal. In Touch Point Approach state, the output signalis zero. In Launch state, the output is a given fraction, say 40% to60%, of pedal position signal and is subject to a minimum value and aprescribed transfer to the given fraction. In Ramp state, the outputgradually increases to the pedal position signal.

Upon vehicle starting with the vehicle stationary or nearly so and theaccelerator pedal depressed, the Touch Point Approach state prevailsuntil the clutch closes to the touch point. Then, if the pedal positionis below 25% of its full travel, the control will be in creep mode andthe filter will be in the Direct state. However, if the pedal is above25%, the filter will be in Launch state and will ramp the output signalto the set fraction of the pedal position signal and then hold at thatfraction until engine deceleration is sensed, indicating that the clutchcapacity has reached a substantial value. That triggers the Ramp stateand causes the output signal to gradually increase to the pedal positionsignal. The starting sequence is then complete. This process allows anorderly application of throttle or other torque control signal to theengine which is appropriate for the pedal and clutch conditions andwhich does not allow the engine to overspeed due to insufficient clutchcapacity. In no event is the throttle filter output greater than thepedal position signal.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other advantages of the invention will become moreapparent from the following description taken in conjunction with theaccompanying drawings wherein like references refer to like parts andwherein:

FIG. 1 is a schematic diagram of a transmission driven through a clutchby an engine and an engine and clutch controller for carrying out theinvention;

FIG. 2 is a curve of clutch torque as a function of clutch position;

FIG. 3 is a diagram of a clutch control logic block showing the inputsand the outputs;

FIG. 4 is a bubble logic diagram for the clutch control logic of FIG. 3;

FIG. 5 is a diagram of a throttle filter logic block showing the inputsand the outputs;

FIG. 6 is a bubble logic diagram for the throttle filter logic of FIG.5; and

FIGS. 7 and 8 are diagrams showing the pedal position and engine controlsignals for a step pedal input and a ramp pedal input, respectively.

DESCRIPTION OF THE INVENTION

FIG. 1 illustrates in schematic form the drive train of a motor vehicleincluding the automatic clutch controller of the present invention. Themotor vehicle includes engine 10 as a source of motive power. For alarge truck of the type to which the present invention is mostapplicable, engine 10 would be a diesel internal combustion engine. Anaccelerator pedal 11 controls operation of engine 10 via throttle filter12. Typically the torque control input to such an engine is a throttlefor controlling air supply, although another control parameter such asfuel supply can be used instead. In any event, the throttle filter 12 isused to supply a torque control signal to the engine in response to theaccelerator pedal 11. Throttle filter 12 is part of the clutchcontroller 60 and filters the throttle signal supplied to engine 10 bylimiting the pedal 11 signal in some cases to a lower value. Engine 10produces torque on engine shaft 15. Engine speed sensor 13 detects therotational velocity of engine shaft 15. The actual site of rotationalvelocity detection by engine speed sensor may be at the engine flywheel.Engine speed sensor 13 is preferably a multitooth wheel whose toothrotation is detected by a magnetic sensor.

Friction clutch 20 includes fixed plate 21 and movable plate 23 that arecapable of full or partial engagement. Fixed plate 21 may be embodied bythe engine flywheel. Friction clutch 20 couples torque from engine shaft15 to transmission input shaft 25 corresponding to the degree ofengagement between fixed plate 21 and movable plate 23. Note that whileFIG. 1 illustrates only a single pair of fixed and movable plates, thoseskilled in the art would realize that clutch 20 could include multiplepairs of such plates.

A typical torque verses clutch position function is illustrated in FIG.2. Clutch torque/position curve 80 is initially zero for a range ofengagements before initial touch point 81. Clutch torque risesmonotonically with increasing clutch engagement. In the exampleillustrated in FIG. 2, clutch torque rises slowly at first and then moresteeply until the maximum clutch torque is reached upon full engagementat point 82. The typical clutch design calls for the maximum clutchtorque upon full engagement to be about 1.5 times the maximum enginetorque. This ensures that clutch 20 can transfer the maximum torqueproduced by engine 10 without slipping.

Clutch actuator 27 is coupled to movable plate 23 for control of clutch20 from disengagement through partial engagement to full engagement.Clutch actuator 27 may be an electrical, hydraulic or pneumatic actuatorand may be position or pressure controlled. Clutch actuator 27 controlsthe degree of clutch engagement according to a clutch engagement signalfrom clutch actuation controller 60. Clutch actuator 27 is a closed loopdevice that controls the degree of clutch engagement to cause themeasured clutch position from clutch position sensor 28 to follow theclutch engagement signal. Touch point determination preferably employsthe measured clutch position from clutch position sensor 28. Thoseskilled in the art would realize that clutch actuator 27 may be pressurecontrolled by a clutch actuation signal corresponding to the desiredclutch pressure and employ clutch pressure feedback measured by a clutchpressure sensor.

Transmission input speed sensor 31 senses the rotational velocity oftransmission input shaft 25, which is the input to transmission 30.Transmission 30 provides selectable drive ratios to drive shaft 35 underthe control of transmission shift controller 33. Drive shaft 35 iscoupled to differential 40. Transmission output speed sensor 37 sensesthe rotational velocity of drive shaft 35. Transmission input speedsensor 31 and transmission output speed sensor 37 are preferablyconstructed in the same manner as engine speed sensor 13. Where themotor vehicle is a large truck, differential 40 drives four axle shafts41 to 44 that are in turn coupled to respective wheels 51 to 54.

Transmission shift controller 33 receives input signals from pedal 11,engine speed sensor 13, vehicle brake 14 pedal, transmission input speedsensor 31 and transmission output speed sensor 37. Transmission shiftcontroller 33 generates gear select signals for control of transmission30 and clutch engage/disengage signals coupled to clutch actuationcontroller 60. Transmission shift controller 33 preferably changes thefinal gear ratio provided by transmission 30 corresponding to thethrottle setting, engine speed, transmission input speed andtransmission output speed. Transmission shift controller 33 providesrespective engage and disengage signals to clutch actuation controller60 depending on whether friction clutch 20 should be engaged ordisengaged. Transmission shift controller also transmits a gear signalto clutch actuation controller 60. This gear signal permits recall ofthe set of coefficients corresponding to the selected gear. Transmissionshift controller 33 preferably briefly engages inertial brake 29 duringupshifts. This slows the rotational speed of transmission input shaft 25to match that of drive shaft 35 before engaging the higher gear. Touchpoint determination preferably employs inertial brake 29 in a mannerthat will be described below. The transmission shift controller 33 formsno part of the present invention and will not be further described.

Clutch actuation controller 60 provides a clutch engagement signal toclutch actuator 27 for controlling the position of movable plate 23.This controls the amount of torque transferred by clutch 20 according toclutch torque/position curve 80 of FIG. 2. Clutch actuation controller60 operates under the control of transmission shift controller 33.Clutch actuation controller 60 controls the movement of moving plate 23from disengagement to at least partial engagement or full engagementupon receipt of the engage signal from transmission shift controller 33.In the preferred embodiment it is contemplated that the clutchengagement signal will indicate a desired clutch position. Clutchactuator 27 preferably includes a closed loop control system employingthe measured clutch position from clutch position sensor 28 forcontrolling movable plate 23 to this desired position. It is alsofeasible for the clutch engagement signal to represent a desired clutchpressure with clutch actuator 27 providing closed loop control to thisdesired pressure.

The control function of clutch actuation controller 60 is needed onlyfor clutch positions between touch point 81 and full engagement. Clutchengagement less than that corresponding to touch point 81 provide nopossibility of torque transfer because clutch 20 is fully disengaged.Upon receipt of the engage signal from transmission shift controller 33,clutch actuation controller 60 preferably rapidly advances clutch 20 toa point corresponding to touch point 81. This sets the zero of theclutch engagement control at touch point 81. Thereafter the clutchengagement is controlled by the control function of clutch actuationcontroller 60.

It is already known to determine the touch point of a clutch, eitherduring operation or in advance. It is preferred to determine the touchpoint in advance by a test process which identifies the clutch positionor a clutch pressure where the touch point occurs. The touch pointprocess is fully disclosed in the U.S. patent application Ser. No.07/815,501, filed Jan. 2, 1992, entitled "Touch Point Identification forAutomatic Clutch Controller", which is assigned to the assignee of thisinvention and is incorporated herein by reference. This process ispreferably a subset of the control function of clutch actuationcontroller 60.

Determination of the touch point involves putting transmission 30 inneutral and applying inertial brake 29. Inertial brake 29 is normallypresent to aid in matching the rotational speed of transmission inputshaft 25 to that of drive shaft 35 during upshifts. Because clutch 20 isdisengaged during the shift the amount of braking needed is very small.Inertial brake 29 need only develop a braking torque of about 5% of theidling engine torque. Clutch 20 is progressively engaged while engine 10is idling until the transmission input speed reaches a predeterminedfraction of the engine idle speed. This degree of clutch engagement,corresponding to point 83 of FIG. 2, transfers torque through clutch 20to overcome the slight braking torque of inertial brake 29. A small,fixed offset 85 is subtracted from this degree of clutch engagement todetermine the touch point 81.

FIG. 3 is a diagram showing the inputs and outputs of clutch modecontrol logic which is a subset of the clutch actuation controller 60.The logic establishes modes according to engine and transmissionoperating conditions and is used in the control of clutch actuation, andis also used in the operation of the throttle filter. The inputs to thelogic are signals representing engine speed (E_(s)) from sensor 13,input speed (I_(s)) from sensor 31, accelerator pedal position frompedal 11, and a touch point signal produced when the clutch positionreaches the predetermined touch position. The logic output is one offive modes set forth below.

Touch Point Approach Mode

Here the clutch is commanded to go to the touch point. When leaving theAuto Mode Off state due to a pedal signal exceeding a minimum threshold,this mode is in a waiting state in which the clutch is beginning toclose, but the touch point has not yet been attained. If the clutch hadalready been engaged, the degree of engagement will be reduced to thetouch point. No engine control signal will be allowed in this mode.

Creep Mode

This mode is established when the touch point is attained and the pedalsignal is above the minimum level (3%) but below a threshold value, say25%. During creep mode the clutch engagement is controlled to cause theinput speed to smoothly approach a percentage of engine speed therebycausing the clutch to slip to allow slow vehicle maneuvers. As set forthin the prior patent applications, mentioned above, the input speed iscontrolled to a creep speed reference signal R_(crp) =E_(s) (T/T_(ref)),where E_(s) is measured engine speed, T is the throttle signal, andT_(ref) is a reference constant equal to the throttle signal for 25%full throttle. The engine control signal (throttle signal) will be equalto the pedal signal in this mode.

Startup Mode

This mode is activated when the pedal signal reaches or exceeds thethreshold value (25%) and is maintained so long as the pedal signal orengine speed remains high, but is terminated when clutch slip becomessmall. In this mode, the principal management of the control signaloccurs as described below. The clutch is contolled to engage at a ratedependent on the engine speed to smoothly advance the input speed to theengine speed. The term "Launch Mode" has sometimes been applied to thismode but here "Startup Mode" is preferred to distinguish from "LaunchState", defined below.

Lockup Mode

This mode is normally entered from the startup mode when clutch slipbecomes small. In this mode the clutch control signal fully engages theclutch. It is exited only when engine speed and pedal signal become lowand/or when vehicle brakes are applied. This mode terminates thethrottle filter function and the control signal will equal the pedalsignal.

Auto Mode Off

One of the above four modes is active when the clutch controller is inan automatic mode. Auto Mode Off is active when there is no suchautomatic operation. Typically, the pedal signal will be at or near zeroor the engine speed will be near idle. No control signal is outputduring this condition and the clutch is commanded to fully disengage.

A bubble diagram in FIG. 4 illustrates the clutch mode control logic.Specific numbers are given in the diagram as an example applicable to aparticular engine/transmission combination. Other numbers areappropriate in other applications. Each number refers to the decimalfraction of full scale or maximum value of the parameter indicated. Forexample, 0.25 or 25% of full pedal movement is selected as the ceilingof the Creep Mode and the beginning of the Startup Mode. Engine idlespeed is 0.25; thus the value 0.27 is chosen to represent a certainspeed above idle, and an engine speed less than 0.188 is approaching astall condition. Also, to be sure that a low throttle signal isintentional, it is required that the system shall treat any pedal valueless then 3% or 0.03 as a zero signal.

The diagram of FIG. 4 is entered in the Auto Mode Off condition. Whenthe pedal signal exceeds 0.03, the Touch Point Approach Mode isactivated. When at Touch Point Approach Mode, if the pedal signal dropsbelow 0.03 and the brake is applied, the mode returns to Auto Mode Off.From Touch Point Approach no action occurs until the touch point TPoccurs and the pedal signal is greater than 3%, and then Creep Mode isactivated. If the engine speed approaches a stall condition the logicreturns to Auto Mode Off, or if the pedal signal drops below 3% itreturns to Touch Point Approach. Normally, the controller stays in theCreep Mode for small pedal signals, but if the pedal signal exceeds 25%,the Startup Mode is entered. If the engine speed becomes less than 0.3and the pedal signal is less than 0.1, the Creep Mode is reentered. Ifthe engine speed nears stall, the logic returns to Auto Mode Off.However, in the case of a successful clutch engagement, the clutch slipbecomes small (E_(s) -I_(s) <0.03) and if the engine speed remains aboveidle the Lockup Mode is entered. The controller will remain in LockupMode unless the pedal is released and the engine speed drops below its"above idle" point; then it will go to Touch Point Approach Mode. If thebrake signal is present in addition to pedal release and engine speeddrop below its "above idle" point, the controller will go to Auto ModeOff.

The block diagram for the throttle filter 12 or the throttle state logicis shown in FIG. 5. The inputs comprise four clutch control modes--TouchPoint Approach, Startup, Creep, and Auto Mode Off--as well as pedalposition and engine acceleration. The outputs are four throttle logicstates--Direct State, Touch Point State, Launch State, and Ramp State.The engine control signal function for each state is defined in thetable below.

    ______________________________________                                        FILTER STATE     CONTROL SIGNAL                                               ______________________________________                                        Touch Point      Zero                                                         Direct           Equal to Pedal                                               Launch           Ramp or Hold to % Pedal,                                                      then Hold at % Pedal                                         Ramp             Ramp to Pedal                                                ______________________________________                                    

The bubble logic diagram of FIG. 6 is entered in the Direct State. Ifthe Touch Point Approach Mode is active, the Touch Point State isselected. In Touch Point State, either Creep Mode or Auto Mode Off willreturn the logic to Direct State. From either the Direct or the TouchPoint State, if the Startup Mode is active, the Launch State isselected. In the Launch State, if the Startup Mode terminates the logicgoes to the Direct State. Otherwise the Launch State is maintained untilengine deceleration, which occurs when the clutch capacity has increasedenough to handle the engine torque. Then the Ramp State is selected. Thelogic returns to the Direct State when the control signal reaches itsmaximum value or exceeds the pedal signal, or the Startup Mode turnsoff.

The operation of the throttle filter is illustrated in the graphs ofFIGS. 7 and 8. FIG. 7 shows a condition of a step input to theaccelerator pedal so that the pedal signal quickly goes to 100%. Sincethe pedal signal is greater than 3%, the clutch control logic goes toTouch Point Approach Mode and the throttle logic goes to the Touch PointState which allows no engine control signal. When the touch point TPoccurs, the clutch control logic goes to the Creep Mode but immediatelyenters the Startup Mode because the pedal signal is greater than the 25%threshold and the Launch State is selected; that is, the clutch controlmode logic process is completed before the throttle logic selects astate and therefor the Direct State is not invoked. The Launch staterequires the control signal to ramp up at some specified rate until itreaches a given fraction, say 60%, of the pedal signal and then holdthat fraction. In this example the pedal is at 100% so the controlsignal ramps up to 60% and holds. If at time x the clutch capacitybecomes sufficient to pull down the engine speed, the throttle logicactivates the Ramp State which commands the control signal to graduallyramp up at a given rate to the pedal signal value. Eventually the clutchslip becomes very small and the clutch control changes from Startup Modeto Lockup Mode, completing the clutch closure. Since the Startup Mode isoff, the throttle logic changes from Ramp State to Direct State,terminating the filter function.

In the FIG. 8 example, the accelerator pedal is gradually applied. Atthe touch point TP the pedal signal is less than 25% so that the CreepMode and the Direct State are invoked, causing the control signal tofollow the pedal signal until the pedal reaches 25% and the Startup Modeand Launch State are invoked. Because the control signal is alreadylarger than 60% of the pedal signal, the control signal is held constantuntil the 60% condition is satisfied at time w. Then it follows the 60%line until time x when engine deceleration is detected and the RampState is entered to provide the final ramp of the control signal.

It will thus be seen that the control method establishes a control ofthe engine during clutch engagement in a way that prevents engineoverspeeding and is also consistent with the clutch operation so thatvehicle acceleration during the launch condition is smoothly carriedout, and also allows full implementation of a creep mode at low pedalpositions.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. In a vehicle having agear transmission including an input shaft driven through a frictionclutch by an engine that is controlled by an accelerator pedal, andhaving a clutch actuation controller for actuating the friction clutch,wherein the friction clutch has engageable parts which initially touchand then progressively increase in torque transfer during actuation, theclutch actuation controller having automatic modes including touch pointapproach mode, creep mode, startup mode and lockup mode, and an automode off state; the method of controlling the engine speed during clutchclosing comprising the steps of:measuring engine speed, transmissioninput speed, and pedal position and producing corresponding signals;initiating operation in the auto mode off state, wherein the clutch isdisengaged; changing from the auto mode off state to the touch pointapproach mode when the pedal position is above a minimum; in touch pointapproach mode controlling the clutch to a touch point; determining thetouch point when the engageable parts of the clutch initially touch;entering a creep mode when the touch point is attained and the pedalposition signal is below a threshold; when in creep mode, generating acontrol signal equal to the pedal position signal; entering the startupmode when the clutch touch point is attained and the pedal positionsignal exceeds the threshold value; when in startup mode generating acontrol signal comprising a fixed percentage of pedal position signal;and controlling the engine speed in accordance with the control signal.2. The invention as defined in claim 1 including the steps of:sensing alow clutch slip from the engine speed and the input speed, and enteringlockup mode when low slip occurs; and in lockup mode, completing theclutch actuation to full engagement.
 3. The invention as defined inclaim 2 including the steps of:in startup mode, monitoring engine speedduring clutch closing to detect speed pulldown; entering a ramp statewhen engine speed pulldown is detected; and when in ramp state,gradually increasing the control signal by increasing the fixedpercentage of the pedal position signal.